Patterns of biodiversity and endemism on Indo-West Pacific coral reefs

Diversity of the primary groups of contemporary Indo-West Pacific coral reef organisms, including mantis shrimps (stomatopod crustaceans), peaks in the Indo-Australian Archipelago (IAA), reaches a lower peak in East Africa and Madagascar [Indian Ocean continental (IOC)], and declines in the central Indian Ocean (IO) and Central Pacific (CP). Percent endemism in stomatopods (highest in the IAA, high in the IOC, lower in regions adjacent to centers, and moderate in the CP) correlates positively with species diversity (this varies with scale) and inversely with species body size. Because it constrains reproductive traits and dispersal, body size is a reliable indicator of speciation and extinction potential in reef stomatopods and probably most marine organisms. Assemblages are dominated by small-sized species in the IAA and IOC. Both speciation and extinction likely are high, resulting in especially high endemism (small ranges reflect both originating and disappearing species) in these regions. Rates of speciation exceed extinction, yielding centers of diversity (especially in the IAA). Dispersal slows speciation and extinction in areas adjacent to these centers. Body size declines toward the CP, especially in atoll environments. Here the wheels of speciation and extinction again spin rapidly but in the opposite direction (extinction > speciation), yielding low diversity and moderate endemism. We conclude that life histories, dispersal, and speciation/extinction dynamics are primary agents that mold patterns of diversity and endemism. Historical factors, currents, productivity, and species diversity itself (through ecological interactions) also influence these patterns, in some cases by altering body size.